Recent evidence suggests that components of attention may serve as early indicators of the onset of dementia of the Alzheimer type (DAT). For example, work from our current Project indicates that higher-level aspects of attentional control are deficient in the earliest stages of the disease, and that these control systems contribute to the observed memory changes. However, to date there has been relatively little work investigating systematic changes in the specific components of attention with age and DAT or the consistency of these components within individuals across different attentional measures and testing sessions. The goal of the present proposal is to target specific components of attention, and provide individual attentional profiles in an attempt to distinguish healthy aging from the earliest stages of Alzheimers Disease. The data obtained from these experiments will also be especially useful in evaluating recent evidence indicating that within-individual variability can serve as a marker for discriminating healthy aging from early stage DAT. In addition, recent evidence suggests that components of attention may be differentially affected by distinct personality types. Hence, personality traits based on the five-factor model of personality will be explored in relation to distinct attentional profiles, disease onset, and disease progression. The proposed experiments will isolate four distinct components of attention: maintenance, selection, switching, and divided attention. Based on the extant literature, three experiments will be designed to tap each of the four components of attention, yielding a battery of 12 attentional tests. Factor analytic procedures will be used to determine whether these tasks load on the predicted attentional components. In addition, we will include a brief standardized attention battery that has been recently developed (Attention Network Test) to investigate its relationship to the targeted components of attention in the present set of experiments. Seven groups of subjects will be tested during Years 1-3 in the proposed attention battery: young adults, middle-aged relatives of a DAT individual, middle-aged controls, healthy young-old adults (mean age 70 years), healthy old-old adults (mean age 85 years), very mild DAT (CDR 0.5) and mild DAT (CDR 1) individuals. In Years 4-5, approximately 70% of these individuals will be retested to provide a replication of the factor structure from Wave 1 testing and to examine the consistency of performance within individuals across testing sessions. In conjunction with data from the remaining Cores and Projects, the data from this project will serve as a cognitive marker to differentiate healthy aging from the earliest stages of the disease process.